You can keep other city's garbage or provide them with water for money.
Venice was one of the two Italian cities that monopolized trade with the far east.
You need to specify which two cities you are referring to if you want to make it possible to answer your question.
Cities in which country or region? There are hundreds or even thousands of cities which could reasonably be called ancient, and you can bet that most of them were on trade routes. Cities existed then, and still mostly do now, because they were centers for trade. Go pick any two old cities reasonably near each other, you can be sure they had a trade route between them (unless they had some barrier like impassible mountains in between).
They made both cities two important harbours for trade
People and ideas also end up being exchanged when distant cities trade products.
The two I know of for sure ar Manchester and Liverpool
Genoa and Venice
shared trade
Through shared trade
i dont know sorry :(
Timbuktu and Gao
through shared trade